How much do sloths sleep?
Sloths in the wild only sleep for 8 – 10 hours per day. The myth that sloths sleep all day long has manifested over decades of casual observation and a bad reputation.
Sloths and sleep: the origin of the myth
The name “sloth” translates as a form of “lazy” in almost every language on our planet. Sloths have been burdened with their bad reputation since they were first described in the scientific literature in 1942 as “the lowest form of existence”.
Before the development of modern animal-tracking technology, scientists trying to understand wild animal behavior had to rely on opportunistic observations. They would simply watch and learn. While this basic approach may work for many species, sloths are unfortunately not one of them.
Sloths are slow-moving, shy, and secretive creatures that are almost impossible to observe for any length of time in the wild. They simply melt into the rainforest canopy and quickly become indistinguishable from the leaves and branches that surround them. They are masters of invisibility.
We now also know that sloths have the same favorite sleeping spots that they will often return to throughout the day and night – interspersed by bouts of activity. A sloth might look like it hasn’t moved from the same place for several days, but it has probably been moving around during the night and has returned back to the same place for a rest. This pattern of behavior has previously tricked curious scientists into believing that sloths can sleep for days on end – something we now know isn’t true at all!
All of this, combined with the myth that sloths are “stoned” because of psychoactive properties in the leaves they eat, has garnered them with an unfair reputation for being lazy.
The problem of studying sloths in captivity
Due to the difficulties associated with studying sloths in the wild, the vast majority of research into sloth behaviour and sleep has been conducted on captive sloths.
It is becoming increasingly accepted that animal behavior in captivity can not be assumed to be the same for their wild counterparts. For example, in zoos and rescue centers, sloths don’t have to forage for the perfect leaves, worry about behavioral thermoregulation, or remain on high-alert for predators.
In addition, without the use of invasive and expensive methods, it is very difficult for an observer to differentiate between ‘sleep’ and ‘rest’. Taking these factors into account, it’s highly likely that the amount of time wild sloths spend sleeping is different from their wild counterparts.
How we measure sleep in sloths?
Sleep can be accurately measured by using an electroencephalogram (EEG), which records brain activity, and an electromyogram (EMG) which detects electric impulses occurring within muscle tissues.
These devices have been used on wild sloths in the past, but they are extremely invasive and likely disturbed the sloths normal behaviour.
Through our Sloth Backpack Project, we are utilizing the latest in micro-datalogger technology to record every tiny movement in wild sloths – from ascending and descending trees, to chewing and yawning. We are generating data that can be used to determine the sloths’ activity budget in a much less invasive way.
Using our backpack data, and comparing it with historical data collected by the use of EEG and EMG studies, we estimate that wild sloths sleep for 8-10 hours per day.
What is ‘inactive rest’?
While sloths don’t spend all day sleeping, this does not mean they are active either. They actually spend the majority of their waking hours in something that we like to call ‘active rest’ – they are not sleeping, but they are completely inactive and often have their eyes closed.
Sloths have the lowest metabolic rate of any non-hibernating mammal and the vast majority of their diet is leaf-based. Leaves themselves do not contain many calories, and due to their slow metabolism, the sloth’s caloric requirement per day is also very low (approximately only 100-150 calories per day!).
This means that sloths do not need to spend much time running around looking for food. Instead, they spend as much of the day as they can in an inactive state (which is easily perceived as sleep) in order to conserve energy and avoid detection by predators!
Read More: Why are sloths so slow?